Inhibition of peroxide formation in ethers



Patented Oct. 4, 1938 UNITED sures INHIBITION OF PEROXIDE FORMATION IN ETHERS Theodore Evans, Berkeley, Calif., assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing. Original application August 17,

1936, Serial No. 96,473. Divided and this ap plication May 3, 1938, Serial No. 205,754

9 Claims.

This invention relates to the stabilization of aliphatic ethers and it more particularly relates to a method of inhibiting the formation of oxidative impurities, as peroxides, in aliphatic ethers,

particularly aliphatic mixed ethers and aliphatic symmetrical isoethers. The invention also relates to stabilized compositions consisting of or comprising aliphatic mixed and/ or aliphatic symmetrical isoethers.

The aliphatic ethers, particularly the mixed ethers and symmetrical isoethers, when stored under ordinary storage conditions, even in glass containers, undergo considerable deterioration whereby the ether is contaminated with oxidative and other decomposition products which materially decrease its value for many commercial purposes. In some cases, due to their high peroxide content, further treatment, as distillation, of the stored ether or ether composition is hazardous. The ethers on standing usually deteriorate by reacting with oxygen to form peroxides, which in turn by interaction and/or spontaneous decomposition may yield aldehydes, ketones, acids and other impurities, the removal of which is in many cases a difiicult and costly proceeding. The impurities formed in the aliphatic mixed ethers and the aliphatic symmetrical isoethers by spontaneous deterioration or auto-oxidation when such ethers are stored or shipped alone or in admixture with one or more other materials, may for convenience be termed oxidative impurities. This term is intended to embrace peroxides, aldehydes, ketones, acids and related contaminating impurities. The deterioration of the aliphatic mixed and aliphatic symmetrical isoethers in-,

creases with lapse of time and is usually favored by: the presence of oxygen in the storage or shipping container; the presence, as is usual, of dissolved oxygen in the ether as manufactured; exposure to light, particularly direct sunlight; exposure to heat; exposure to air; exposure to pressure and the like.

It isan object of my invention to provide a practical and highly effective method for substantially inhibiting the formation of peroxides and other deleterious impurities in the ethers to which this invention relates when the same, either in the pure state or in admixture with other materials as hydrocarbons and the like, are stored, shipped or used for purposes where a stable ether or ether-containing mixture substantially free of peroxides and other oxidative impurities is desired. i It is another object of my invention to provide 55, novel and useful compositions which are substantially stabilized against deterioration and peroxide formation and which consist of or comprise one or more aliphatic mixed ethers and/or one or more aliphatic symmetrical isoethers. These stabilized compositions may be stored for relatively long periods of time and they may be shipped for great distances, in the conventional containers, without substantial peroxide formation or deterioration of the ether content of the composition. The stabilized compositions are useful for a wide variety of purposes, and they are useful as raw materials in the production of a wide variety of products.

The process of my invention comprises incor porating with the ether to be stabilized, or with the mixture comprising one or more of such ethers, by mixing or any other suitable means, a stabilizing amount of an organic hydroxy amino compound. By the term stabilizing amount, I mean an amount of an organic hydroxy amino compound or mixture of such compounds effective to stabilize the ether content of the treated material against deterioration, for example, against auto-oxidation resulting in peroxide formation.

The ethers stabilized in accordance with the invention are members of the class of ethers consisting of aliphatic mixed ethers and aliphatic symmetrical isoethers. The aliphatic mixed ethers are ethers wherein two difierent aliphatic radicals are linked to an ether oxygen atom. The difierent aliphatic radicals may be straight chain radicals or branched chain radicals or one may be straight chain and the other branched. The radicals may be the residues of aliphatic normalor iso-primary or secondary alcohols or they may be the radicals of aliphatic tertiary alcohols, The simplest aliphatic mixed ether is methyl ethyl ether. Other readily available aliphatic mixed ethers are methyl propyl ether, methyl isopropyl ether, methyl normal butyl ether, methyl tertiary butyl ether, methyl amyl ether, methyl tertiary amyl ether, methyl hexyl ether, methyl tertiary hexyl ether, ethyl propyl ether, ethyl isopropyl ether, ethyl normal butyl ether, ethyl secondary butyl ether, ethyl tertiary butyl ether, ethyl amyl ether, ethyl secondary amyl ether, ethyl tertiary amyl ether, the ethyl hexyl ethers, the propyl butyl ethers, the propyl amyl ethers and the like. The homologues, analogues and substitution products of the above, as well as mixed ethers wherein one or both of the aliphatic radicals is/are unsaturated, as for example, ethyl isobutenyl ether, allyl isobutenyl ether, ethyl isopentenyl ether, and the like, may

be stabilized in accordance with the invention. The aliphatic mixed ethers possessing a methyl group linked to an ether oxygen atom as the methyl butyl ethers, etc. are usually more stable than the higher mixed ethers possessing radicals containing at least two carbon atoms. Under some conditions, the former may be sufficiently stable and may not require stabilization. However, the latter are very susceptible to auto-oxidation and must be stabilized if excessive peroxide formation is to be avoided when they are stored for even relatively short periods of time.

In the aliphatic symmetrical isoethers, the aliphatic radicals linked to the ether oxygen atom are identical, and the compound forms a chain at least doubly branched. The aliphatic radicals are the'radicals of aliphatic iso-prirnary alcohols, normalor iso-secondary alcohols or tertiary alcohols. The simplest aliphatic symmetrical isoether is diisopropyl ether, which compoundis particularly susceptible to auto-eoxidation with the formation of peroxide. After standing for a short period of time, diisopropyl ether usually contains sufficient peroxide to render its purification bydistillation, without a previous treatment to destroy the peroxide, extremely hazardous due to dangers of explosion.

Other readily available aliphatic symmetrical isoethers which may be stabilized in accordance with the invention are: diisobutyl ether, disecondary butyl ether, ditertiary butyl ether, diisoamyl ether, the disecondary amyl ethers, ditertiary amyl ether, diisohexyl ether and the like and their homologues and substitution products. The aliphatic unsaturated symmetrical isoethers as diisobutenyl ether, diisopentenyl ether, disecond ary pentenyl ether and the like may be stabilized in accordance with the invention.

The ether stabilizing agents or peroxide-formation inhibiting agents used in accordance with the invention are organic hydroxy amino compounds. The term organic hydroxy amino compound is used herein and in the appended claims to embrace those organic compounds of aliphatic,

aralkyl or alicyclic character which contain at least one hydroxy group and at least one amino group to the molecule.

Suitable representative organic hydroxy amino compounds are the'following: the alkylolamines as monomethanolamine, dimethanolamine, trimethanolamine, monoethanolamine, the diand tri-ethanolamines, the mono-, diand tri-normalpropanolamines and isopropanolamines, the butanolamines, the pentanolamines, the hexanolamines, etc; the aldehyde-ammonias as acetaldehyde ammonia, isobutyraldehyde ammonia, benzaldehyde ammonia and the like; the aralkylolamines; the aromatic hydroxy amino compounds as p-amino phenol, o-amino phenol, m-amino phenol, the methyl amino phenols, the ethyl amino phenols, diethyl-m-amino phenol, nitro-aminophenol, the

diamino phenols, triamino phenol, the amino cresols, the amino naphthols, the amino anthrols and the like and their homologues, and suitable substitution products. If desired, mixtures of different species of organic hydroxy amino compropionaldehyde ammonia,

use as much as 3% or more of the stabilizing agent. The amount of the inhibitor to be used to stabilize the ether or ether mixture to the desired extent will usually be dependent upon the particular stabilizing agent, upon the particular ether or ether combination to be stabilized and upon the conditions to which the stabilized material will be subjected. In the majority of cases, organic hydroxy amino compounds have the desired effectiveness when employed in concentrations of from about 0.002% to about 2% by weight of the ether content of the material stabilized.

The organic hydroxy amino compound may be added to the ether to be stabilized in any desired manner. The inhibitor compound may be added per se or suspended or dissolved in a suitable medium. It isfin general desirable to select the specific organic hydroxy amino compound with respect to the ether or ether composition to be stabilized so that the former is soluble to the desiredextent in the latter. It may also in some cases, be desirable to select the specific inhibitor with respect to the material stabilized so that it may, if desired, be subsequently separated therefrom by some convenient means as distillation, extraction, etc.

The material stabilized may consist of one or more aliphatic ethers of the class consisting of aliphatic mixed ethers and aliphatic symmetrical isoethers. The inventionalso embraces within its scope the stabilization against deterioration.

and peroxide formation of the ether content of mixtures comprising one or more of such ethers in substantial amount. The ether or ethers may be in admixture with one or more solvents or diluents, as the following; the aromatic and aralkyl hydrocarbons as benzene, toluene, xylene, cymene, ethyl benzene, etc. the alicyclic hydrocarbons as cyclohexane, tetrahydrobenzene, etc.; the satu-' rated as well as unsaturated aliphatic hydrocarbons; the hydrocarbon mixtures as gasoline, kerosene, Diesel oil, fuel oil, lubricating oil, etc. halogenated hydrocarbons and various oxycompounds as alcohols, esters and the like.

To measure the rate of peroxide formation in some readily available aliphatic mixed ethers and aliphatic symmetrical isoethers on storage, and to demonstrate the efiectiveness of representative organic hydroxy'amino compounds in inhibiting peroxide formation, a series of tests were made, the results of which are given in the following examples. It is to be understood that the examples areforpurposes of illustration; the in vention is not to be regarded as limitedto the specific ethers stabilized nor to the specific organic hydroxy amino compounds recited.

Example I spectively. One of the samples was left untreated to serve as a blank. The p-amino phenol and ethanolamine were added to the samples in an amount corresponding to about 0.004 mol of inhibiter per liter of ether stabilized. The sample bottles were closed with stoppers provided with capillary tubes to permit the contents of the bottles to have access to the atmosphere, and the bottles stored'in a darkcabinet for six months.

At the end of this time the contents of" the bot-,

Ethyl tertiary butyl." Do

0c. N/20 thiosulphate per 2 cc. ether 'Ether Inhibitor V Titration after 6 months Initial titration Ethyl tertiary butyl Do Acetaldehyde-ammonia.

These results show that while a considerable amount of peroxide wasformed in the untreated sample, there was no peroxide formation at all in the stabilized samples.

Example II Four samples of ethyl tertiary butyl ether of about equal volume were placed in bottles as described in Example I. The sample in one bottle was stabilized by the addition thereto of p-amino phenol, another sample was stabilized with monoethanolamine, another was stabilized with acetaldehyde-ammonia, and the fourth was untreated. In the stabilized samples, the organic hydroxy amino compound was used in an amount corresponding to about 0.004 mol of inhibitor per liter of ether. The samples were stored in a dark cabinet for 12 months. At the end of this time the peroxide content of the samples was determined by the method described in Example I. The results were as follows:

tion in ethyl tertiary amyl ether stored in metal or glass containers.

Grams peroxide oxygen/liter ether Samples After 3 After 7 months months Stored in tin cans:

200 cc. ether-mo inhibitor 0. 32 l. 04 200 cc. ether+0.2 cc. monoethanolamine 0. 04 0. 03 Stored in glass:

cc. ether-n0 inhibitor 1.28 100 cc. ether+0.05 cc. monoethanolamine 0. 07

Example V The following table shows the effectiveness of a representative alkylolamine in inhibiting peroxide formation in diisopropyl ether stored in glass containers.

Equivalents peroxide oxygen per liter of ether Samples 3 months 7 months 10 months 100 cc. ether-no inhibitor 0. 097 0. 0.28 100 cc. ether-+0.05 cc. monoethanolamine 0. 0062 0. 0062 0. 0062 While I have described my invention in a detailed manner and provided examples illustrating modes of executing the same, it is to be understood that modifications may be made and that no limitations other than those imposed by the scope of the appended claims are intended.

This application is a division of my copending agplication, Serial No. 96,473, filed August 17, 1 36.

I claim as my invention:

1. A composition of matter stabilized against peroxide formation which comprises an aliphatic mixed ether and a stabilizing amount of an organic hydroxy amino compound of the group consisting of para-amino phenol, acetaldehydeammonia and ethanolamine.

Cc. N [20 thiosulphate/2 cc. ether Titration after 12 mo.

Atoms of peroxide oxygen per liter of ether after 12 months Acetaldehyde-ammonia.

Example III Two samples of 200 cc. each of the same stock of ethyl tertiary amyl ether were placed in tin cans. The contents of one of the cans was stabilized against peroxide formation by the addition thereto of about 0.2 cc. of monoethanolamine. The cans were stoppered and stored for 96 days. At the end of this time the peroxide content of each sample was determined.

The untreated sample contained 0.32 gm. of peroxide oxygen per liter of ether, while the stabilized sample was found to be free of peroxide.

Example IV The following table shows the effectiveness of monoethanolamine in inhibiting peroxide forma- 2. A composition of matter stabilized against peroxide formation which comprises an ethyl butyl ether and a stabilizing amount of an organic hydroxy amino compound of the group consisting of para-amino phenol, acetaldehyde-ammonia and ethanolamine.

3. A composition of matter stabilized against peroxide formation which comprises an ethyl propyl ether and a stabilizing amount of an organic hydroxy amino compound of the group consisting of para-amino phenol, acetaldehydeammonia and ethanolamine.

4. A composition of matter stabilized against peroxide formation which comprises an ethyl amyl ether and a stabilizing amount of an organic hydroxy amino compound of the group cionsistin'g ,of para-amino phenol, acetaldehydeammonia and ethanolamine.

5. A composition of matter stabilized against peroxide formation which comprises an aliphatic mixed ether of the group consisting of ethyl tertiary butylether and ethyl tertiary amyl ether and a stabilizing amount of an organic hydroxy amino compound of the group consisting of paraamino phenol, acetaldehyde-ammonia and ethanolamine.

6.. A composition of matter stabilized against peroxide formation which comprises an aliphatic mixed ether of the group consisting of ethyl tertiary butyl ether and ethyl tertiary amyl ether and a stabilizing amount of ethanolamine.

' '7. A composition of matterstabilized against peroxide formation which comprises ethyl tertiary butyl ether and a stabilizing amount of an organic hydroxy amino compound of the group consisting of para-amino phenol; acetalde'hyde ammonia and ethanolamine; V

8.. A composition of matter stabilized against 

